1. Field of the Invention
The present invention relates to a photoelectric conversion element, an image reading device, an image forming apparatus, and an image reading method.
2. Description of the Related Art
Known image reading devices, such as scanners, include a photoelectric conversion element that performs a photoelectric conversion on light that is reflected by an original document; an analog processing unit that performs an operation for an AD conversion on an analog signal output from the photoelectric conversion element; and an image correction unit that performs various corrections on image data that has been converted into digital signals. Conventionally, CCDs are often used as the photoelectric conversion element; however, CMOS linear image sensors have been recently popular due to the demands for a higher speed and a lower electric power. Nowadays, it is known that a plurality of pixels is treated as one group (column) of pixels and a processing circuit is provided for each column.
However, conventional CMOS linear image sensors, which perform an operation on a per-column basis, need to temporarily hold analog signals and sequentially read them according to a one-shot exposure method. To hold an analog signal, an element needs to have capacitances depending on the holding time. Specifically, there is a problem that it is difficult to reduce the size of CMOS linear image sensors. Furthermore, conventional CMOS linear image sensors have a problem that, if an analog signal is not held according to a sequential exposure method, the image quality is degraded due to a color shift and/or the like.
In consideration of the foregoing, there is a need to provide a photoelectric conversion element, an image reading device, an image forming apparatus, and an image reading method to achieve both a reduction in the size of an element and a prevention of a degradation in the image quality.